Sized paper



Patented July 11, 1950 OFFICE SIZED PAPER Robert N. Woodward, Roch'e'steiyN. Ya, assignor to Eastman Kodak Company, Rochester, N. Ye, a corporation ofNew Jersey hid-Drawing. Application Nouember 7, 1946,

Serial-No. 708,457

3 Claims.

This invention relates to'aprocess for prestrength imparting resin a catalyst, usually in the nature of an inorganic salt of acidic tendencies. Y

One object of my invention is to provide a catalytic material in the sizing forpaper which is efiective, not only with the resin, but also for the accompanying sizing material used. Another object of my invention is to provide a paper suitable for use for photographic purposes, which is free of frilling. Other objects of my invention will appear herein.

I have found that when citric or tartaric acid is employed as the catalyst in sizing material for paper that the paper which is sized therewith is free of frilling in contrast to other papers prepared using inorganic catalysts.

Paper is tested as toits frilling properties by first coating it with a layer of a 5% gelatin solution containing a small proportion of formaldehyde to act as a hardener therefor. The coating is dried, and the coated paperc'i's then soaked in water a predetermined time. 'Thefgelatin coating is scratched, and the frilling is determined .by running ones finger down the scratch. If any of the coating rubs off, frilling is not satisfactory, the degree of frilling being measured by the length of scratch where the coating rubs off. Whereas paper sized using various inorganic catalysts exhibited some frilling, none of the products obtained when paper was sized with sizing materials using citric or tartaric acids exhibited any frill.

The size is applied to the paper, preferably as a surface sizing, such as by passing the paper through a solution of the sizing materials and drying. In one method of sizing, paper is formed and dried and then passed through a dilute solution (or suspension) containing starch, watersoluble, wet-strength imparting resin and citric or tartaric acid at the rate of, for instance, 90-200 feet per minute, and again drying, such as with heated calender rolls. Another method of sizing 2 the paper is by passing it while in wet form as it comes'from the paper machine (prior to calendering) through the sizing bath, 'followed' by drying with calenderrolls.

Although papers generally .Inay besized in accordance with my invention, I have jffoundmy sizing method is particularly useful for sizing waterleaf paper, such as prepared from high alpha-cellulose pulp, particularly'for paper having a high degree of permanence. My invention is particularly directed to thesizingof paper for photographic purposes. In carrying out'my in-- vention it has been found desirableto employ the starch in dilute aqueous solution, such as 148% concentration obtained by boiling the desired amount of 'starch in water. also incorporated in the sizing solution is the water-soluble resin, prefer-ably'inan amount 10-50% of the starch and enough-citric and/or tartaric acidto reduce the pH of the sizing solution to a value withii'i the ra'ngeof 3-5. t

Paper prepared in accordance with my inven- -tion may be used to make photographic paper by applying directly thereto, a layer o'f-a light-sensitive silver halide emulsion, "the protective vehicle being gelatin, far-hydrolyzed cellulose acetate, polyvinyl "alcohol or any'o'f the materials known to be useful for this purpose. If desired, the paper may first be given'abaryta coating and the photosensitive emulsion layer is then applied thereover. However, it is an advantage of my paper that it may be coated with the emulsion directly and the emulsion permanently adheres thereto.

"Citric and tartaric acids have both been found to not only catalyze -the -further resinificationbf the resins employedbut also to have a pronounced hardening effector-1 the s'tarch-employed-in con-- trast to the inorganic salts which have been previously employed in this connection. The sole criterion of the amount of citric or tartaric acid to employ is the reduction of the pH to a value within the range 3-5. It is necessary that the amount of citric and/or tartaric acid be at least 1% of the weight of the starch present, but ordinarily the amount used will be somewhat greater.

After the paper has been sized, it is dried, preferably by passing it over heated calendering rolls (such as at a temperature of 190 F.). In this operation not only is the water driven off, but also, hardening and increasing of the water-resistance of the sizing materials takes place. The resulting paper is much more resistant to the softening action of water than a like paper prepared with an inorganic acid catalyst.

least ten Samples of waterleaf (unsized) paper were tub sized by the following compositions, were allowed to dry and were tested for frilling by placing thereon a dyed, hardened gelatin layer, drying, soaking in water and running the test. A decided improvement was noted over previously sized papers in which an inorganic catalyst was used.

Composition No. I

1000 parts of water 40 parts of starch 8 parts of water-soluble melamine-formaldehyd citric acid to reduce pH to 4.

Composition No. II

Same as I only tartaric acid (instead of citric).

Composition No. III

1000 parts of water 40 parts of starch 8 parts of acid-soluble melamine-formaldehyde citric acid to reduce pH to 5.

Composition No. IV

1000 parts of water 40 parts of starch 8 parts of urea-formaldehyde resin 'citric' acid to reduce pH to 5.

Composition No. V

1000 parts of water 7 40 parts of starch 8 parts of urea-formaldehyde-polyvinyl alcohol resin citric acid to reduce pH to 4.

A sample of Waterleaf paper of the same type as sized in the preceding examples was sized with a composition like Composition No. I except that alum instead of citric acid was employed to reduce the pH to 4. This paper was tested for frilling by the test described above. Although after a soaking time to five minutes no frilling occurred, the paper exhibited frilling after soaking for at minutes. Papers prepared in ac- .cordance with my invention were tested at the :same time and under the same conditions and rexhibited no frilling even though the soaking was allowed to run for as much as an hour.

The melamine-formaldehyde resins which are employed in the above examples are those known in the trade as Papermakers resins No. 607. The use of these resins in the tub-sizing of paper is described in U. S. Patents Nos. 2,291,079 and 2,291,080, of Hofferbert. Urea-formaldehyde resins useful in making paper are marketed under the name Uformite, the use of resins of this type in paper manufacture having'been disclosed in British Patents Nos. 502,855 and 502,856 of Moss. I

The starch which is employed in my invention may be any of the starches commonly employed in paper making, such as corn-starch, potato starch, etc. 'Usually a cooked starch is used in paper sizing so as to provide the proper fluidity for application to the paper.

Iclaimi I l 1. Paperwhich is free offrilling when used for photographic purposes which results from the surface sizing of waterleaf high a-cellulose paper with a composition essentially consisting of aqueous starch of 18% concentration, 10-50% based on the weight of the starch of a watersoluble wetwstrength-imparting resin selected from the group-consisting of melamine-formaldehyde and urea f ormaldehyde resins and an amount of acid selected from the group consisting of citric and tartaric acids sufficient to impart a pH of 3-5 to the solution.

2. Paper which is free of frilling when used for photographic purposes which results from the surface sizing of waterleaf high a-cellulose paper with a composition essentially consisting of aqueous starch of 1'-8%-concentration,- 10-50% based on the weight ofthe starch of a Watersoluble wet strength-impartmg resin selected from th'e group consisting of urea-formaldehyde and melamine-formaldehyde resins and a suf ficient amount of citric acid to impart a pH of 3-5 .to the solution.-

3. Paper which is free of frilling when used for photographic purposes which results from the surface sizing of waterleaf high acellulose paper with a composition essentially consisting of aqueous starch of 1-8% concentration, 10-50% based on the weight of the starch of a watersoluble' wet strength-imparting melamine-formaldehyde resin andsufiicient citric acid to impart a pH of 3-5 to' the solution.

- r ROBERT N. WQODWARD.

' .REFERENCES CITED The following references are of record in the file of this patent: 

1. PAPER WHICH IS FREE OF FRILING WHEN USED FOR PHOTOGRAPHIC PURPOSES WHICH RESULTS FROM THE SURFACE SIZING OF WATERLEAF HIGH A-CELLULOSE PAPER WITH A COMPOSITION ESSENTIALLY CONSISTING OF AQUEOUS STARCH OF 1-8% CONCENTRATION, 10-50% BASED ON THE WEIGHT OF THE STARCH OF A WATERSOLUBLE WET STRENGTH-IMPARTING RESIN SELECTED FROM THE GROUP CONSISTING OF MELAMINE-FORMALDEHYDE AND UREA-FORMALDEHYDE RESINS AND AN AMOUNT OF ACID SELECTED FROM THE GROUP CONSISTING OF CITRIC AND TARTARIC ACIDS SUFFICIENT TO IMPART A PH OF 3-5 TO THE SOLUTION. 